Systematic approach to leptogenesis in nonequilibrium QFT: self-energy contribution to the CP-violating parameter

TL;DR

This paper employs the Schwinger-Keldysh/Kadanoff-Baym formalism to accurately compute the self-energy contribution to the CP-violating parameter in leptogenesis, addressing limitations of traditional Boltzmann approaches and highlighting medium effects.

Contribution

It introduces a systematic, double-counting-free method using nonequilibrium QFT to analyze leptogenesis, revealing linear medium corrections and breakdown of Boltzmann approximation in resonant regimes.

Findings

Medium effects increase the CP-violating parameter.

Medium corrections are linear in particle densities.

Boltzmann approximation fails in maximal resonant regime.

Abstract

In the baryogenesis via leptogenesis scenario the self-energy contribution to the CP-violating parameter plays a very important role. Here, we calculate it in a simple toy model of leptogenesis using the Schwinger-Keldysh/Kadanoff-Baym formalism as starting point. We show that the formalism is free of the double-counting problem typical for the canonical Boltzmann approach. Within the toy model, medium effects increase the CP-violating parameter. In contrast to results obtained earlier in the framework of thermal field theory, the medium corrections are linear in the particle number densities. In the resonant regime quantum corrections lead to modified expressions for the CP-violating parameter and for the decay width. Most notably, in the maximal resonant regime the Boltzmann picture breaks down and an analysis in the full Kadanoff-Baym formalism is required.